US3270702A

US3270702A - Ship stabilizer comprising weirs

Info

Publication number: US3270702A
Application number: US386187A
Authority: US
Inventors: Sheldon B Field
Original assignee: John J Mcmullen Associates Inc
Current assignee: John J Mcmullen Associates Inc
Priority date: 1964-07-30
Filing date: 1964-07-30
Publication date: 1966-09-06
Anticipated expiration: 1983-09-06
Also published as: FI43689B; DE1456266B1; NL6509887A; NO122821B; GB1070508A

Description

Sept. 6, 1966 s. B. FIELD SHIP STABILIZER COMPRISING WEIRS Filed July 30. 1964 F ig,

Fig.2

INVENTOR She/don 5. Field ATTORNEYS United States Patent 3,270,702 SHIP STABILIZER COMPRISING WEIRS Sheldon B. Field, Floral Park, N.Y., assignor to John J. McMullen Associates, Incorporated, New York, N.Y., a corporation of New York Filed July 30, 1964, Ser. No. 386,187 5 Claims. (Cl. 114-125) The present invention relates generally to a ship stabilizer and more particularly an improved apparatus for applying a restoring moment by the movement of fluid Within a tank.

Ships of practically every type encounter the problem of undesirable ship motion caused by the surface condition of water. Depending upon the type and size of the ship and the operating conditions to which the ship is to be subjected, various hull designs are selected to counteract the tendency of the water to impart motion to the ship. Due to the great number of variables present and since cyclic wave motion can cause a gradual increase in the energy of motion of the ship, hull design provides only a limited effect in controlling the ship motion. Other attempts to minimize ship motion in response to wave action include the provision of stabilization systems which are capable of applying a restoring moment to the ship when it is subjected to the motion. Particular emphasis has been made with respect to improving systems for minimizing roll. Ballast tanks connected by piping and the like have been employed in order to transfer water in a manner to generate a restoring moment. Such systems encounter the diflicu-lty of maintaining the proper phasing between the restoring moment and motion imparted to the ship. Efforts to employ volumes of air above liquid ballast for controlling the ballast have resulted in massive systems which are uncertain as well as excessively noisy in operation. Efforts have also been directed to providing the ship with fin members extending from the hull beneath the water line and adapted to generate restoring moments from the hydrodynamic forces on the fins accompanying the motion of the ship. In certain applications controlled fins have been effective in controlling the roll of the ship but only with the expense of complex systems employing massive fin members and operating machinery. Furthermore, controlled fins are generally effective only when the ship is underway and therefore cause drag resulting in a loss of ship speed.

Accordingly, it is the primary object of the present invention to provide a ship stabilizer which is cap-able of applying a restoring moment to the ship whether the ship is underway or stationary.

More particularly, it is an object of the invention to provide a ship stabilizer which is passive, that is, a stabilizer which applies the restoring moment directly in response to the movement of the ship about the axis about which the ship is to be stabilized without the need of control equipment.

Furthermore, it is an object of the invention to provide a ship stabilizer in which the movement of fluid in response to the movement of a ship is sufficiently opposed in order that the fluid can apply a restoring moment to the ship.

Another object of the invention is to provide a ship stabilizer which is passive in operation but which is adapted to be conveniently adjusted to compensate for changes in the condition of the ship or the sea.

A still further object of the invention is to provide a ship stabilizer which is relatively compact and of reasonable weight.

A further object of the invention is to provide a ship stabilizer which damps the movement of fluid therein so that better stability can be imparted and the degree of roll of the ship is held to a minimum.

In one embodiment of the invention the ship stabilizer 3,270,702 Patented Sept. 6, 1966 comprises a tank containing a quantity of fluid having a free surface. The longitudinal axis of the tank is adapted to extend substantially horizontally and substantially at right angles to the axis about which the ship is to be stabilized. Thus, if the ship is to be stabilized against roll, the tank is disposed in a substantially athwar-tship direction along one of the decks of the ship. In order to oppose the flow of fluid from one portion of the tank to the other, a plurality of weirs or hydraulic jumps are mounted in the bottom of the ship at substantially right angles to the direction of movement of fluid within the tank.

Further and other objects of the invention will be understood from the following description when viewed with respect to the drawings, in which:

FIGURE 1 is a vertical sectional View of a ship showing the arrangement of the ship stabilizer;

FIGURE 2 is an enlarged plan view of one embodiment of the stabilizer;

FIGURE 3 is a vertical section view of the stabilizer taken along lines 33 of FIGURE 2;

FIGURE 4 is a perspective view of the stabilizer shown in FIGURES 2 and 3.

Referring to the figures in detail, there is shown in FIGURE 1 a ship stabilizer generally indicated as stabilizer 10 mounted athwartship below decks 12 of the ship 14. It can be seen,'when the stabilizer 10 is partially filled with fluid, said stabilizer can perform passive stab-ilization whenever roll forces are applied to the ship 14. The stabilizer comprises a tank 16 formed by

sides

18 and 20 and

ends

22 and 24. The tank 16 can have a top to prevent fluid spill or the sides can extend between two decks, thus using the upper deck as a top. By extending the stabilizer across the hull of ship 14 the maximum moment arm of the liquid can be obtained. The stabilizer is proportioned in a manner such that the weight of the liquid which is displaced in a position adjacent an end portion thereof is suflicient to generate a restoring moment capable of restoring the motion of the ship for a range of sea conditions. The fluid within the tank has a free surface and can move in response to the motion of the ship. It can be seen, however, that once the moment force is created by the liquid to oppose the roll of the ship, the fluid mass velocity increases so that the fluid mass begins to move across the tank to the opposite end thereof. As will be described below, a portion of the kinetic energy of the moving mass will be absorbed by the hydraulic jumps or weirs 216 and 2 8 so that a large reflected wave will not result. The

upstanding weirs

26 and 28 are mounted perpendicular to the direction of flow of the fluid within the tank and also function to impede or dampen the flow of fluid therein.

The fluid to be employed within the stabilizer can be any liquid or the like having suflicient density and with a viscosity of a sufliciently low magnitude so that flow can readily take place within tank 16. Liquids such as sea water, fresh water, bunker oil or types of liquid cargo can be used in the stabilizer tank. Once the stabilizer has been designed in the ship, the depth of the fluid within the stabilizer tank can be varied for tuning the stabilizer to various conditions of the ship and sea.

In order for a restoring moment to be generated, it is necessary that the moment be substantially out of phase with the forces applied to the ship by th sea. Thus, in the case of roll, as the crest of the wave strikes along one side of the ship, the force resulting from the moment must be applied in opposition to the force of the wave. After the wave causes the ship to roll, it is necessary that the moment be reversed so that the force is applied to the opposite side of the ship.

The operation of the stabilizer will now be described. Let it be assumed that a wave strikes the ship such that the ship rolls to elevate side 30 and lower side 32. As side 30 rises, the impedance imparted to the fluid in tank 16 by

weir

26 and 28 oppose the flow of fluid from end portion 34 in the direction toward end portion 36. As side 30 approaches its maximum point of upward movement, a hydrostatic head is formed within the stabilizer so that flow of fluid takes place over the top of weir 26 and the fluid mass flows towards end portion 36. The potential energy of the fluid is maximum at the maximum elevation of side 30 and the Weight of the hydrostatic head imparts a restoring moment force to the ship. The potential energy of the fluid in end portion 34 is converted into kinetic energy as the fluid mass begins to flow over weir 26 toward end portion 36. After side 30 is lowered and the ship passes through a level position, the fluid continues to flow in the direction of end portion 36 due to its kinetic energy. In this way, it is seen that there is an accumulation of fluid in end portion 36 as the portion of the hull adjacent thereto attempts to be elevated by the sea or rolling forces. As the mass of fluid arrives at end portion 36, a portion of the kinetic energy thereof is absorbed by the weir or jump 2 8, and also, an impedance to a reflected wave is also imparted to the fluid by said weir 28. Thus, weir 28 prevents an immediate reversal of fluid flow as side 32 of the ship rises so that fluid can present a restoring moment in opposition to the rising side 32. This process then continues so long as sea forces are applied to the bull to cause it to move about and roll about the axis of the ship.

It should be understood that the number of weirs or the cross section configuration of the weirs can be changed without departing from the spirit of this invention. Said cross section can be triangular, rectangular, trapezoidal, or any other desired shape.

It should also be understood that the height of Weir 276 and height of Weir 28 can be made adjustable by any conventional means in accordance wit-h the desired liquid level present in tank 16 without departing from the spirit of this invention.

While there has been disclosed what at present is considered to be a preferred embodiment of the invention, it is to be understood that changes and modifications can be made therein without departing from the essential spirit of the invention. The scope of the present invention should only be limited by the scope of the appended claims.

What is claimed is:

1. A ship stabilizer comprising an elongated containing means partially filled with a liquid body, the top surface of which is in a free surface condition, said containing means having a bottom, sides and a longitudinal axis, said containing means including two upstanding weir means each mounted off-center toward opposite ends within said containing means, said weir means having a height less than that of said sides, said weir means disposed substantial-1y perpendicular to said longitudinal axis and contacting said sides and said bottom of said containing means, and that portion of said containing means between said two weir means comprising a substantially unobstructed flume.

2. The apparatus as claimed in claim 1 wherein said elongated containing means comprises a substantial flat bottom, two vertical uniplanar sides, and two ends; said bottom, two sides and two ends forming a flume tank of a substantially constant cross-section throughout.

3. The apparatus as claimed in claim 2 wherein said flume tank includes only said two weir means mounted transverse said longitudinal axis and olf-center toward opposite ends of said tank, said weir means spaced from said two ends and from each other.

4. The apparatus as claimed in claim 3 wherein said two weir means comprise two upstanding plates in contact relation with said bottom and said sides of said tank, and wherein the tops of said plates have rounded edges.

5. The apparatus as claimed in claim 4 wherein the heights of said plates are related to the level of liquid in said tank in accordance with the desired periodic movement of liquid Within said tank.

References Cited by the Examiner UNITED STATES PATENTS 2,077,143 4/1937 Carroll 114-425 3,083,672 4/ 1963 Ripley 114125 3,083,674 4/1963 Ripley 114-125 3,160,136 12/1964 Ripley l14125 FOREIGN PATENTS 688,796 3/1940 Germany.

OTHER REFERENCES Ser. No. 132,695, Hort (A.P.C.), published May 1943.

MILTON BUCHLER, Primary Examiner.

T. M. BLIX, Assistant Examiner.

Claims

1. A SHIP STABILIZER COMPRISING AN ELONGATED CONTAINING MEANS PARTIALLY FILLED WITH A LIQUID BODY, THE TOP SURFACE OF WHICH IS IN A FREE SURFACE CONDITION, SAID CONTAINING MEANS HAVING A BOTTOM, SIDES AND A LONGITUDINAL AXIS, SAID CONTAINING MEANS INCLUDING TWO UPSTANDING WEIR MEANS EACH MOUNTED OFF-CENTER TOWARD OPPOSITE ENDS WITHIN SAID CONTAINING MEANS, SAID WEIR MEANS HAVING A HEIGHT LESS THAN THAT OF SAID SIDES, SAID WEIR MEANS DISPOSED SUSBTANTIALLY PERPENDICULAR TO SAID LONGITUDINAL AXIS AND CONTACTING SAID SIDES AND SAID BOTTOM OF SAID CONTAINING MEANS, AND THAT PORTION OF SAID CONTAINING MEANS BETWEEN SAID TWO WEIR COMPRISING A SUSBTANTIALLY UNOBSTRUCTED FLUME.